The present invention relates generally to electrical power outage detection apparatus, and more particularly, to power supplies and power monitors for use with electrical and electronic loads requiring an orderly shutdown in the event of a power outage.
While the invention has use in many electronic systems where an electrical load, such as a computer, must be controlled, it finds particular application in metering systems for powering and controlling electronic meters and electronic microprocessor based registers.
For several years, electronic registers have been installed on conventional induction type watthour meters for registering electrical energy consumption. In a meter of this type, a pulse initiator provides pulses proportional to electrical energy consumption to an electronic register which accumulates and stores the pulses as data representative of such consumption. This data can then be retrieved periodically by a utility company meter reader and used to bill the consumer.
There are various types of electronic registers in use in meters today, two of which are the well known time of use register and the demand register. Both of these registers generally have a micro computer or processor which stores the accumulated meter data in a volatile memory. During normal operation, if power to the electronic register is lost, or interrupted for a sustained period the data in the volatile memory can be lost. Thus, it can be seen that a need exists to prevent this loss of data.
The time of use register usually employs its own power supply and a battery back-up system for supplying the necessary bias voltages to the register during the period of a power outage to prevent the loss of data in its volatile memory. This type of register usually contains a circuit which detects a power outage or low voltage condition from its power supply for switching in the battery back-up system. When a power outage is detected, the register's micro processor usually goes through an orderly shutdown procedure to place the register in a low power mode whereby battery back-up voltage is provided to only those register circuits necessary for time keeping and the preservation of the meter data; namely the register's clock calendar and its volatile memory.
The electronic demand register, like the time of use register, also usually contains its own power supply for providing the necessary bias voltages to the register circuits. However, unlike the time of use register, the demand register does not have a battery back-up system. Instead, the electronic demand register employs a non-volatile data storage or memory for receiving and storing data from the register's micro processor volatile memory when a power outage is detected by the register. The data is thus preserved during the power outage and can be written back to the volatile memory upon the restoration of power to the demand register's power supply.
In the electronic demand register, it takes its microprocessor a certain period of time to read the data from its volatile memory and write that data to the non-volatile memory. During this period of time, the necessary bias voltages must be sustained at their proper levels to allow the microprocessor to carry out its memory read/write functions. U.S. Pat. No. 4,591,782, assigned to the assignee of the present invention, discloses an electronic demand register which includes a power supply and power monitor that enables the microprocessor to carry out these functions.
U.S. Pat. No. 4,591,782 discloses an electronic demand register which receives pulses proportional to power consumption from a conventional induction type watthour meter. The register includes a microprocessor, a volatile memory and a non-volatile memory. The register also includes its own power supply, power monitor and power fail detect circuitry for signalling the microprocessor of a power outage. Upon the receipt of a power fail detect signal, the microprocessor enters into a read/write cycle to transfer data from its volatile memory to the non-volatile memory. As previously mentioned, it takes a certain period of time to complete the transfer of data into the non-volatile memory. The power supply and monitor contains a storage capacitor which stores a sufficient quantity of electrical energy to sustain a regulated DC voltage to the register at its normal value for the period of time required to carry out the transfer of the data into the non-volatile memory.
While the system disclosed in the aforementioned patent works well in its intended application it has certain limitations and cost disadvantages. One limitation is that the power supply, monitor and storage capacitor can accommodate only a single light load imposed by the demand register. In addition the demand register's complexity and cost is increased by the incorporation therein, of the power supply, monitor, storage capacitor and power fail detect and timing circuitry necessary to carry out the aforementioned read/write functions. In certain applications, enhanced system performance and manufacturing cost advantages can be realized by removing this complexity from the demand register (including other types of electronic registers and controllable loads) and designing it into a less complex universally useable power supply and monitor which can provide sufficient voltage and current during a power outage to a drive either a single load, such as a demand register, or a plurality of loads.
An application example of where the above performance and cost advantages can be achieved is in a fully electronic metering system. Fully electronic watthour meters are directly replacing the conventional induction type watthour meter in certain applications. These electronic watthour meters monitor energy consumption and provide data pulses proportional to energy consumption to an electronic register in a manner similar to the induction type watthour meter.
An electronic watthour meter, unlike the conventional induction type meter, requires a power supply for supplying the proper bias voltages to the meter circuits. These bias voltages can also be used by the circuits in an electronic register which receive pulses representative of energy consumption from the electronic meter.
Thus, it can be seen that a need exists for a universally useable power supply and monitor which can be used to supply operating voltages and currents to a plurality of loads, such as an electronic meter and an electronic register, and which can sustain the voltages applied to these loads for a prescribed period of time following a power outage to enable an orderly shutdown of at least one load.